


something dangerous and true

by nilchance



Series: ain't this the life [7]
Category: Undertale (Video Game)
Genre: M/M, Praise Kink, Topping from the Bottom, Underfell Sans, cross-universe bullshit shenanigans, kustard - Freeform, offscreen fellcest
Language: English
Status: Completed
Published: 2018-05-15
Updated: 2018-05-15
Packaged: 2019-05-07 14:33:53
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,605
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14673126
Author URL: https://archiveofourown.org/users/nilchance/pseuds/nilchance
Summary: If Sans was exactly like Red, they’d get along better. If Sans was exactly like Red, Red probably wouldn’t want to bang him like a screen door in a hurricane. He’s always been a big fan of chaos theory.





	something dangerous and true

Sans has issues.

Granted, that was hard to miss starting from the second that Sans let Edge put a weapon in his face without ever losing that plastic smile. But Sans has control issues and that was a surprise.

If Red let him, Sans would try to control the whole scene every time they fucked. He'd be nice about it. He’d make sure that Red had a good time. That's Sans's thing, making sure the other guy has a good time. His other thing is making sure that nothing happens to wipe the cool, bullshit grin off his face.

It’s Sans’s turn to steer. He could have anything. He could fuck Red’s mouth and come down his throat. He could put him on his hands and knees, push Red’s face into the couch cushions, and take what he wants. Hell, he could tentacle-fuck Red until he was a wrecked, exhausted puddle, although Red’s starting to wonder if Sans even knows he could do that. He’s never fucked a skeleton monster before Red and doesn’t seem to realize the only limit on magic junk is its owner’s creativity, or depravity, or both.

Sky’s the limit. But what Sans does is put himself on his knees between Red's legs on the couch, his mouth on Red's cunt. There’s nothing submissive about it. He eats Red out like he's planning to do it for hours, unhurried and deliberate. His mouth is sweet and languid, his hands pinning Red's hips flat against the couch to keep him in place. It's a move that Sans would never let Red get away with, not without a lot of trying to fast-talk his way out of it.

That's all right. Red'll get him back next time.

Or this time, if Red plays his cards right.

It's good. It's almost too good, like Red is some sweet thing who needs to be plied with oral before he can take Sans's cock. He's come once already and he feels like he's spun sugar melting onto Sans's tongue. Seriously, fuck Sans for being so good at this.

Sans's flat tongue circles Red's clit, gliding in all the wet. Red shudders, his back arching, trying to grind against Sans’s face. Can’t get anywhere with Sans holding onto him. Turns out Sans is surprisingly strong. Red whines, “Dude, come on.” 

Sans pull back to ask, his voice husked out like he's been sucking dick, "Problem?"

Red takes advantage of the fact that his leg is slung over Sans's shoulder to whack Sans in the side of the head with his knee. He’s gentle; Sans would be real easy to break, and not in the fun sexy way. Sans gives him a flat look, like his face isn't smeared with wetness and Red is the ridiculous one here. Red says, "I want your dick."

Sans's eyelights flare like a struck match, because he's a sucker for dirty talk and thinks Red doesn't know. But he plays it cool, turning his head to nip the inside of Red's femur with his flat little teeth. "Does that count as a problem now?"

"It does when you won't give it to me," Red says. "You want me to ask nice? I can do that."

Sans's fingers flex on Red's hips. He grins crookedly. "I doubt it."

"Please," Red says. He's never been too good to beg. Sans inhales sharply and Red presses his advantage. "Now fuck me."

Sans shrugs Red's leg off his shoulder. Lightly, he says, "Hey, who am I to tell you no?"

"That's real chivalrous of you," Red says. He lays down on the couch, shifting to make room for Sans between his legs. "C'mere and do me."

Wiping his mouth on the back of his hand, Sans climbs on the couch. His brow is arched like he can compete with Edge when it comes to skeptical expressions. "Missionary position? Really?"

"What can I say? The trapeze is broken and the goat left town," Red says.

"Surely you kid," Sans says. His dick glows a faint blue like the walls of Waterfall, and looks about as hard. Nice and thick at the base. Red never appreciated the aesthetics of his own dick until he saw it on Sans. "Goat-ta put out an APB. That goat was baaaaa'd news."

Red snickers, wrapping his legs around Sans’s hips. "Nice."

Sans flashes him a quick, genuine grin. "Thanks." Then he lines his dick up to slide inside Red, knuckles bumping Red's throbbing cunt. Sans is deliberate. Considerate. Hung up on being a good lay.

"Do it slow," Red says.

Sans stops cold, concerned enough to actually look Red in the face during sex for once. "Something wrong?"

Red grins up at him. "What, you in a hurry all of a sudden?"

"I’ve never been in a hurry in my life. You were the one who wanted to move things along," Sans says. He’s suspicious now, Red can see it on his face. Sans isn’t stupid. Well, all right, sometimes Sans is deeply fucking stupid, but he’s stupid about what he wants and not about people’s motivations.

(Most people’s. It’s not like Edge is being subtle, but Sans would be freaking out a lot more if he realized Edge is trying to get him in the sack.)

With a shrug, Red folds both arms behind his head. Look at how much he’s not interfering. "Hey, I'm just in the mood for some slow, gentle screwing in the missionary posish. Trying to see how the other half lives. You oughta be good for it, you’re boring."

"And you're an asshole."

"You knew that before I laid one goddamn finger on you," Red says. "Don't act all surprised now."

“Next time I’m shoving a sock in your mouth.”

"Big words from Mr. 'I'm So Vanilla I Jizz Softserve.'" Sans snorts. Red coaxes, "C’mon. Don’t you wanna show me a good time? Ain’t that why we’re taking turns like nice, civilized people?”

Sans rolls his eyes. Then he grabs Red's hip and pushes a little inside him, like he's testing the angle to see if it works. It does. Red's wet enough to make it so damn easy, and Sans is still hard for all his endless, pointless bitchery. 

Sans buries his face in Red’s shoulder and hisses through his teeth like it hurts, a noise that's lost under Red's groan. All the shame's been burnt out of him by Edge, who won't accept anything less than Red ruined and begging for it. He can't turn it off for Sans, and he wouldn't if he could.

And oh, Sans pushes into him with a slowness that verges on passive-aggressive, like Red can go ahead and choke on how slow this is. It doesn't hurt. He's used to a certain amount of burn, likes it that way, and it's weird to have nothing but this slick, sweet stretch. Edge would never fuck him like this.

(He would never let Edge fuck him like this.)

He grabs Sans's shoulders to have something to hold onto, hating the stupid t-shirts more than he's ever hated a piece of clothing. Red wants to see what Sans thinks he's hiding. Sans made himself Red's problem. He doesn't get to hide.

By the time Sans is all the way inside, they're both a mess. Red wants to rut against him until they're both sticky and satisfied, but this? Listening to Sans’s shaky breathing as he fights himself because Red told him to? Totally worth it. He just wishes he could see Sans’s face.

“Gimme a sec,” Red says. Sans does, pressed inside him all tense and trembling.

"D-" Sans falters, swallows and tries that again. He almost manages to sound unaffected. Almost. "Do you have to moan like a porn star?"

"Yeah," Red says, dragging the word out. He grips the back of Sans's neck in one hand, digging his fingers into the wire tension that lives there. Dude needs to relax before he hurts himself. "You got me all messed up."

Sans lets out a shuddery breath. Then he redirects, biting Red's collarbone. It's nowhere near as hard as Edge would do it, won't even leave a mark, but it's a nice jolt to the system. Red clenches down on him hard and Sans’s breath hitches. Then Red wraps a leg around him, rocking himself a little on Sans's dick. Says, "'M digging this slow vanilla missionary thing. Move."

"Pushy," Sans says, amused and indulgent, and gives him what he wants.

Is this how Edge feels every time Red goes down on his knees for him, this smug bone-deep satisfaction? Because Red could definitely get used to this. He’s not used to getting exactly what he asked for.

Red lifts his hips so Sans can fuck him at a better angle. When it hits just right, Red sighs, “Yeahhh, that’s the stuff.”

“Glad to hear it,” Sans says. Red can hear the smirk in his voice. He thinks he’s the one is charge because Red’s the one with a dick in him. That’s adorable.

Red reaches between their bodies to get his fingers on his clit. He can come just from being fucked, but it takes more roughness than he thinks Sans is going to give him tonight. What’s already good gets better. He must tighten down on Sans again, because Sans makes a stifled noise against his shoulder. Red digs his fingers into Sans’s shoulder and breathes, “Shit. Keep fucking me just like that.”

Nuzzling him, Sans says, “Nobody likes a backseat driver.”

Red laughs, and it turns into a groan halfway through. “Yeah, I can feel how much you don’t like me.”

“It’s a hate boner,” Sans says. His unconcerned act doesn’t quite work with the way he sounds strained and unsteady, his breathing hot against Red’s shoulder. He doesn’t lose rhythm, though. It’s impressive.

Six years without fucking. Sans responds to Red touching him like he’s starved for it, desperate and sweet, and he’s had all that time on his knees to get pent up. This whole slow ride thing must be making him crazy, but he’s keeping his shit together. He was wasted on the idiots he used to fuck, all that need and skill and desire to be useful. It’s fucking tragic.

“Funny,” Red says. “For a guy who hates me, you’re being real sweet to me right now.”

If Red didn’t have his hands on him, he wouldn’t feel the shiver run down Sans’s back. Sans says, “You think I don’t know what you’re doing?”

“You don’t have to listen to me,” Red says.

“I do if you never shut the fuck up.”

“Then take what you want,” Red says. His body is winding up fast, and he eases off his clit for a minute to hold it off. He isn’t done with Sans yet. Not even close. “Oh, but that’d mean admitting that you want things, wouldn’t it?”

“I can’t believe I fuck you,” Sans mutters.

Red laughs, reaching further down his body to where Sans is fucking into him. “You can’t?”

The fleeting graze of Red’s fingers on the base of his dick drags a moan out of Sans, like that light touch is too much for him to keep quiet. Sans’s hips jerk forward for just a second and Red groans from the bottom of his soul. 

“Fuck,” Sans says, dragging himself back into line. His shirt is sticking to his spine with sweat, and his back will probably be killing him tomorrow. He’s trembling. “Fine.”

“There you go.” Red puts his newly slicked fingers back on his clit. A few strokes and he’s almost as keyed up as he was before he stopped. He can’t drag this out as long as he’d like to. He’s no good at self-denial. "You're being so good for me."

He's just being a dick, rubbing it in Sans’s face a little. He doesn't expect Sans to freeze, a noise slipping through his clenched teeth.

Oh shit. Is it Gyftmas? It must be Gyftmas.

“Hey.” Red grips the back of Sans's neck in case he gets any ideas about tweaking out. "That okay?”

He doesn’t want to ask. He wants to hammer on this shiny new vulnerability until it breaks off, because that’s what he always does. But Sans is skittish and Red’s already pushing him harder than he meant to.

Silence. A long, long silence, long enough that Red thinks maybe he broke him. Then Sans says almost too quietly to hear, “Yeah.”

Sans is a judgmental, hypocritical, lying asshole with a mean streak. He’s a version of Red, and so Red will always hate him a little. But right now Red feels a couple soft, squishy feelings for him that he’ll deny until the day he fucking dies. It’s the endorphins, clearly, and the power trip of being the one to mess him up. Nothing important.

“Thanks,” Red says. “That’s real good.”

“Shut up already,” Sans says, but there’s no real bite in it. He starts moving in Red again.

“I gotcha, sweetheart." Red doesn't know himself if he's reassuring or just bragging. His free hand keeps rubbing his clit, the pleasure building hot and heavy in the base of his spine. He could go faster, rougher, get himself off hard and quick, but he doesn’t. It’s so unlike the way he usually fucks that it’s kinda looped around into being kinky again. "Keep going. Just a little more. 'M so close. You?"

Sans’s fingers are digging into his hip like he's trying to leave grooves in the bone, a carelessness that says more than words. Red can feel Sans struggling for control with every slow, dirty grind of his hips. Sans says, a catch in his voice, “Sorry, what? I fell asleep up here.”

Damn, he's fun.

“Sternum,” Red says. It’s hard to be eloquent with the way he’s starting to pant for air. Fuck it, Sans knows what he means. Sans takes his hand off Red’s hip to grab his sternum between thumb and forefinger, rubbing along the not-scar that carves across his ribs. He knows the exact angle of it like nobody else would, not even Edge. Red groans, heartfelt. “Fuck, that’s perfect. Don’t stop.”

Sans doesn’t stop. He digs his fingers in, just shy of pain, putting Red’s nervous system back in familiar territory. It shoves Red from ‘close’ to ‘coming’ too fucking fast, and he barely manages to get out the words, “C’mon, hard, give me--”

Sans snaps. He grabs Red’s hip, driving into him, fucking him right through his orgasm. It’s fast and it’s desperate and it’s rougher than Sans has ever been with him. He muffles most of his noises against Red, although what Red manages to hear is so hot it’s gonna be burned into his memory. 

Red can’t seem to shut up, like Sans is driving the words out of him. He claws Sans’s back, overstimulated and twenty kinds of fucked up, nonsense spilling out of his mouth between gasps. “Yeah, honey, take it, just fuck me up, _fuck_ me, it’s good, it’s so good, fuck fuck _fuck_ \--!”

If Sans wasn’t on top of him, pinning him flat, Red would’ve jackknifed with how hard he comes, his spine arching painfully, wringing him out. And Sans, that absolute fucker, manages not to come until after he knows he’s gotten Red off twice. When he does, it’s quiet and almost violent, just the rattle of his bones as he shudders and a ragged moan. Red puts his arms around him and holds him together.

Sans’s shirts are all bunched up between them. While Sans stops shaking, Red slips his hands underneath, moving slow so Sans can tell him no. Instead Sans lets Red feel up the back of his ribcage without a complaint. Red can touch but he can’t look. Good to know.

Sans’s ribs are surprisingly cool to the touch, even with both of them sweating in the afterglow. The bones are smooth, not a single scar on them. Sans tenses up a little when Red runs his fingers across the places he really dug in.

“I can heal those if you want,” Red says, breaking the silence.

“It’s fine,” Sans says, like a total fucking liar. Whatever. Red’s had to deal with overprotective assholes pushing healing on him when he says he’s fine. Sans isn’t dying. He’s not gonna force the issue. Call it angry cripple solidarity or whatever.

… Yeah, Red’s not gonna lie and say he doesn’t like the idea of those marks lingering a while.

Red runs his fingers down the ladder of Sans’s spine, listening to the little click of bone on bone. He can practically hear Sans starting to overthink. Red says, “You took real good care of me.”

"What is good, really?" Sans says, deflecting and not even bothering to do it well. Shit's downright insulting. "It's too subjective to mean anything. There’s no such thing as a universal moral code--"

"Get your dick out of me before you get philosophical," Red says.

Sans does, pausing to drop a last kiss on Red's throat. “Just kidding, murder is still the worst.” Then he sits up and studies Red’s hip. He’s grinning easily, but he’s trying real hard not to meet Red’s eyes. “You think that’ll bruise?”

Red feels it with his fingers. “Nah. Does it matter?”

“Edge thinks so,” Sans says. “Kinda don’t want him to slap my head off my neck. It’s a thing.”

“It’s hilarious how much you think you understand him,” Red says. “‘Cause you really, really don’t. Fair warning.”

“Duly noted,” Sans says, in a tone that says he didn’t hear one goddamn word. Welp. Can’t say Red didn’t try. “If I left marks, just heal them, okay?”

“Fine,” Red says. “Moody bitch.”

He reaches for Sans. Predictably, Sans ducks out of the way and bends to grab his clothes, because Red really wants to play the game where he tries to make Sans hold still for two goddamn seconds again. Sans says, "This was fun and everything but I’m out.”

Of course he’s running.

“Yeah?” Red asks Sans’s back. “Got somewhere important to be?”

Sans doesn’t look at him as he slides his shorts back on. “Everybody’s on my ass about sleeping, so I figured I’d give it a shot.”

“Bullshit,” Red says. Sans shrugs. When Red reaches out and puts his hand low on Sans’s spine where his shirts rides up, Sans stops. His posture is one big bristle, like a cat with its back up. Red wonders if he looks like that just before he turns around and bites Edge’s head off for being too nice to him. Probably. Red says, “Hey, asshole.”

“What,” Sans says.

Lightly, gently, Red strokes his spine with a thumb. Sans shivers. Red says, “You’re real good at making simple shit complicated, ain’t you?”

“Sorry, buddy,” Sans says. “No idea what you’re talking about.”

“Sure you don’t.” Red sits up, pleased with the ache in his cunt where Sans was a little rough with him, and presses himself against Sans’s back. He kisses the place where Sans’s neck meets his shoulder, trailing his mouth up Sans’s throat. Slowly, slowly, the steel slips out of Sans’s spine. Red murmurs against the curve of Sans’s throat, “Who said I was done with you?”

“Well, there was the part where you came three times,” Sans says dryly, like he’s not leaning his head to one side to give Red better access.

“Three times to your one,” Red says. “I think we can do better than that. ‘Cause unless you shoved a glowstick in your pelvis when I wasn’t looking, I think you’re still, heh, up for it.”

“This isn’t a good idea,” Sans says. He does sound tired, but it’s the kind that’s got nothing to do with sleep.

“Probably not,” Red agrees. He takes his fingers off Sans’s spine and leans back, giving him room. Sans’s fingers tighten hard in his hoodie. Red tells him, “Your call. If you wanna go, I’m not stopping you.”

It’s 50/50 whether Sans bolts. They’re the same person by nature, but those years of nurture have introduced enough variation into the system that Red genuinely doesn’t know what he’s gonna do. All the things that made Red cling to the few good things in his shithole life and grab what he wants in both hands didn’t happen to Sans. Sans’s life just made him weird about asking for things, weird about wanting them, weird about letting himself have them.

If Sans was exactly like Red, they’d get along better. If Sans was exactly like Red, Red probably wouldn’t want to bang him like a screen door in a hurricane. He’s always been a big fan of chaos theory.

Sans drops the hoodie. The zipper makes a loud ‘clunk’ when it hits the floor. “No more weird shit or I’m gone.”

“You got a twisted definition of weird shit. Ain’t nothing wrong with wanting somebody to say you’re good once in a while.” Sans says nothing. Red sighs. “You got it. Absolutely no weird shit tonight aside from your regularly scheduled clonefucking.”

"Do interdimensional doubles count as clones?” Sans asks nobody in particular. “We really gotta get the terminology figured out before we send the letter that goes, ‘Dear Penthouse, I never thought it could happen to--’"

The words get lost when Red drags Sans’s head back and bites his throat. Sans whips around, taking Red’s face in his cold hands, kissing him desperately like Red is his last cigarette before the firing squad. Red laughs, and Sans lets Red pull him down.


End file.
